CD4 T Cell Responses in Mycobacterium tuberculosis and HIV Co-infection Open Access

Abstract

Mycobacterium tuberculosis (Mtb) is the infectious agent that causes tuberculosis (TB) disease. TB is the leading cause of death due to a single infectious agent and has remained one of the top 10 causes of death worldwide for decades. In 2017, 10 million new cases of TB disease were reported, resulting in 1.6 million deaths. An estimated 1.7 billion people, representing nearly a quarter of the world’s population, are latently infected with Mtb and therefore at risk for developing active TB disease. Infection with HIV induces immune suppression and depletion of CD4 T cells, which play a critical role in limiting Mtb bacterial growth and reducing progression to active TB disease.

Mtb-specific CD4 T cells in HIV-infected individuals exhibit elements of immune dysfunction, including impaired proliferative capacity, heightened immune activation and cell death, and reduced cytokine production capacity. Using cohorts of HIV-infected and HIV-uninfected individuals with latent and active TB in South Africa and Kenya, two high TB burden countries, we conducted a thorough examination of T cell inhibitory receptor expression profiles on antigen-specific CD4 and CD8 T cells and the upregulation of surface activation-induced markers (AIM) CD25, OX40, CD69 and CD40L on Mtb-specific CD4 T cells. Further, we extended our studies to analyze the effect of HIV co-infection on Mtb-specific cytokine production profiles.

Our findings provide novel evidence that the majority of Mtb-specific CD4 T cells do not co-express multiple inhibitory receptors, regardless of HIV infection status. Our findings also highlight a previously unrecognized role of BTLA expression on Mtb-specific CD4 T cells. In addition, our findings suggest that infection with HIV modifies Mtb-specific cytokine production profiles towards elevated TNF-a production and that AIM assays enable identification of Mtb-specific CD4 T cell responses in a cytokine-independent manner in HIV-uninfected and HIV-infected individuals. Overall, our findings provide a foundation for future studies to further define immune correlates of protection to Mtb and elucidate mechanisms of HIV-associated dysregulation of anti-mycobacterial immunity. 

Table of Contents

LIST OF TABLES AND FIGURES

Chapter 1

Chapter 2

Chapter 3

Appendix

CHAPTER I

INTRODUCTION

The Global Burden of TB

The Global Burden of TB/HIV Co-infection

History of TB

The Pathogen, Transmission, and Replication

Diagnostics

Spectrum of Mycobacterium tuberculosis infection

The Immune Response

The Immune Response to Mtb

The Immune Response to Mtb/HIV Co-infection

Thesis Overview

Figures

Figure 1. Estimated TB incidence rates in 2017 (3).

Figure 2. Projected acceleration in the decline of global tuberculosis incidence rated to target levels

Figure 3. Estimated HIV prevalence in new and relapse TB cases in 2017 (3).

Figure 4. Spectrum of Mtb infection and TB disease (30).

Figure 5. Simplified flow chart of immune functions.

Figure 6. The impact of HIV co-infection on granuloma formation (69).

CHAPTER II

HIV infection is associated with downregulation of BTLA expression on Mycobacterium tuberculosis-specific CD4 T cells in active tuberculosis disease

Abstract

Introduction

Materials and Methods

Results

Study participants

Frequencies of Mtb-specific CD4 T cells producing IFN-g and/or TNF-a are similar in HIV-infected and HIV-uninfected individuals.

Active TB disease is associated with reduced inhibitory receptor co-expression on total CD4 T cells

Mtb-specific CD4 T cell inhibitory receptor expression profiles are modulated in HIV-infected individuals with active TB

BTLA expression is downregulated on Mtb-specific CD4 T cells HIV-infected individuals with active TB

Inhibitory receptor expression on Mtb-specific CD4 T cells differs from HCMV- and HIV-specific CD4 T cells

Discussion

Acknowledgements

Tables

Table I.  Characteristics of study participants

Figure Legends

Figures

Figure 1. Similar frequencies of Mtb-specific T cells producing IFN-γ and TNF-α in HIV-infected and HIV-uninfected individuals with latent and active TB.

Figure 2. Active TB disease is associated with reduced inhibitory receptor co-expression on total CD4 T cells.

Figure 3. Modulation of Mtb-specific CD4 T cell inhibitory receptor expression profiles in HIV-infected individuals with active TB

Figure 4. HIV infection is associated with downregulation of BTLA expression on total CD4 T cells and Mtb-specific CD4 T cells in active TB.

Figure 5. Differential inhibitory receptor expression profiles on Mtb-specific CD4 T cells, compared with HCMV- and HIV-specific CD4 T cells within the same individuals.

Supplementary Figure Legends

Supplementary Figures

Figure S1. Gating strategy for flow cytometry analysis.

Figure S2. Similar frequencies of SEB and HCMV-specific T cells producing IFN-γ and TNF-α in HIV-infected and HIV-uninfected individuals with latent and active TB.

Figure S3. CTLA-4 and PD-1 expression on Mtb-specific CD4 T cells in latent and active TB.

Figure S4. BTLA expression does not correlate with HIV viral load in HIV-infected individuals with LTBI and active TB.

Figure S5. BTLA expression does not correlate with absolute CD4 T cell count in HIV-infected individuals with LTBI and active TB.

Figure S6. Mtb-specific CD4 T cells express higher levels of BTLA and lower levels of CTLA-4 and PD-1, compared with HCMV- and HIV-specific CD4 T cells.

CHAPTER III

Activation-induced marker expression identifies Mtb-specific CD4 T cells with altered cytokine production in HIV-infected individuals with latent TB

Abstract

Introduction

Materials and Methods

Results

Study participants.

Upregulation of AIM markers identifies Mtb-specific CD4 T cells in HIV-infected and HIV-uninfected individuals.

Decreased frequencies of Th1 and Th17 cytokines and increased frequencies of TNF-a produced by Mtb-specific CD4 T cells in HIV-infected individuals.

HIV infection alters the relationship between Mtb-specific CD4 T cell AIM marker expression and cytokine production in individuals with LTBI

HIV infection modifies Mtb-specific cytokine production profiles in individuals with LTBI

Discussion

Acknowledgements

Tables

Table 1.  Characteristics of study participants

Figure Legends

Figures

Figure 1. Differential upregulation of AIM markers on Mtb-specific CD4 T cells from QFT^– and LTBI individuals.

Figure 2. Antigen-specific CD4 T cell AIM assay functionality scores are similar between HIV-infected and HIV-uninfected individuals with LTBI.

Figure 3: HIV co-infection modifies Mtb-specific cytokine production profiles in individuals with LTBI.

Figure 4. Co-infection with HIV skews the relationship between antigen-specific CD4 T cell AIM marker expression and cytokine production profiles in individuals with LTBI.

Figure 5. Comparative analysis of the effect of HIV infection on cytokine profiles in LTBI.

Supplementary Figure Legends

Supplementary Figures

Figure S1. HIV infection is associated with a lower QFT TB Antigen IFN-γ response, compared with HIV-uninfected individuals with LTBI.

Figure S2. HCMV-specific CD4 T cell responses in the AIM assay are not significantly impacted by Mtb and HIV infection status.

Figure S3. HIV infection alters antigen-specific cytokine production profiles in both QFT⁻ and LTBI individuals.

CHAPTER IV

DISCUSSION

Summary of Findings

Conclusions

Future Implications

CHAPTER V

REFERENCES

CHAPTER VI

APPENDIX

Unpublished Data on Inhibitory Receptor Phenotype of Mtb-specific CD8 T cells

Figure 1. Similar frequencies of inhibitory receptor co-expression on total CD8 T cells in HIV-infected and HIV-uninfected individuals with LTBI

Figure 4. Differential inhibitory receptor expression profiles on Mtb-specific CD8 T cells, compared with HCMV- and HIV-specific CD8 T cells within the same individuals

Figure 5. Similar frequencies of inhibitory receptor co-expression on total CD8 T cells in HIV-infected and HIV-uninfected individuals with active TB.

Figure 6. HIV infection is associated with upregulation of CTLA-4 and PD-1 expression and downregulation of BTLA on Mtb-specific CD8 T cells in individuals with active TB disease.

Figure 7. BTLA, CTLA-4 and PD-1 expression on total and Mtb-specific CD8 T cells in individuals with active TB

Figure 8. Differential inhibitory receptor expression profiles on Mtb-specific CD8 T cells, compared with HCMV- and HIV-specific CD8 T cells within the same individuals.

About this Dissertation

Rights statement

• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Laney Graduate School
Department	Biological and Biomedical Sciences
Subfield / Discipline	Immunology and Molecular Pathogenesis
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Biology, Cell Biology, Microbiology
Keyword	T cells Tuberculosis HIV TB Coinfection
Committee Chair / Thesis Advisor	Cheryl L. Day, Emory University
Committee Members	Jyothi Rengarajan , Emory University Rama Amara, Emory University Pat Marsteller, Emory University Joshy Jacobs, Emory University

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